Sept. 4 . 1916 Influence of Barnyard Manure on Soil Bacteria 905 



months. In July much the same order occurs. The soil receiving 15 

 tons of manure per acre contains more bacteria than that receiving 5 tons, 

 and this in turn has more than the unmanured soil. Here the influence 

 of the water becomes very marked, for there are many more bacteria in 

 the soils receiving 10, 20, or 30 inches of water than in the soils receiving 

 either no water or 40 inches. The excessive quantity of water, 40 inches, 

 apparently checks the development of bacteria on the synthetic media. 



The same results, in general, are obtained for November as for May and 

 July, and with the exception of the abnormal results reported, where 10 

 inches of water were applied, the water has a pronounced effect even as 

 late as November. This difference disappears during the winter, for we 

 find a more uniform condition existing the next spring. 



The average results for the unmanured soil show that more bacteria 

 developed from the soil receiving 30 inches of water than from those 

 receiving either more or less irrigation water. The manured soil, on the 

 other hand, gave a maximum count from the soil receiving 20 inches of 

 water. These differences are clearly brought out in figure 3. On the 

 horizontal line is indicated the quantity of water applied, while on the 

 perpendicular is given the number of colonies which developed. At the 

 top of the figure are given the results for the spring, while below this in 

 the order named for midsummer, fall, and the average for the year. 



If we consider the average number of bacteria developing on synthetic 

 media from the unmanured plots as 100 per cent, those developing on the 

 manured plots become, with 5 tons of manure, 147 per cent, and with 15 

 tons, 177 per cent, showing that in so far as numbers are concerned the 

 greatest effect per ton of manure applied is produced by the addition of 

 5 tons per acre. If we average the unirrigated plots and take these as 

 100 per cent, the others become, with 5 inches of water, 81 per cent; with 

 10 inches of water, 106 per cent; 20 inches of water, 107 per cent; 30 

 inches of water, no per cent; and 40 inches of water, 91 per cent. The 

 maximum increase is apparently due to the application of 30 inches of 

 irrigation water. But here, as was the case with the pot experiments, 

 the results are not uniform. 



The same plots were tested for ammonification, the results being given 

 in Table V. In every case the result is the average of a number of closely 

 agreeing determinations and are given as milligrams of ammonia pro- 

 duced in four days in 100 gtn. of soil containing 2 gm. of dried blood. 



The ammonifying powers of the soil, as may be seen from Table V, 

 remain nearly constant throughout the season. There is, however, a big 

 variation in the ammonifying powers of the different soils. In the 

 spring the ammonifying powers of the unmanured soils are low. The 

 quantity of ammonia formed in no case exceeds 57 mgm. per 100 gm. of 

 soil. The water applied apparently had no perceptible influence upon 

 the rate of ammonification. The quantity of ammonia produced by the 

 soil receiving 5 tons per acre of manure is much higher than that pro- 



